1. Field of the Invention
The present invention relates to a manufacturing method and its apparatus for reducing an occurrence rate of picture element imperfections in a panel display.
2. Description of the Related Art
FIG. 1 illustrates a typical configuration of an electrical discharge type plasma display panel. Numbered components indicated in this figure are: sustaining discharge electrodes 1x and 1y; bus electrodes 2x and 2y supplying voltage to the sustaining discharge electrodes 1x and 1y; a dielectric layer 3 uniformly Covering the bus electrodes; a discharge cathode 4 formed with a vaporized MgO film; and a frontal glass substrate 5 loaded with the sustaining discharge electrodes, the dielectric layer and the vaporized MgO film.
Further, the numbered components are: address electrodes 6 intersecting perpendicularly with the sustaining discharge electrodes; a barrier rib 7 for separating the address electrodes 6; fluorescent bodies 8R (red), 8G (green) and 8B (blue) are formed in walls of the address electrodes 6 and the barrier rib 7; a rear glass substrate 9 loaded with the address electrodes, the barrier rib and the fluorescent bodies. A discharge chamber surrounded by the fluorescent bodies and the cathode film 4 is formed at the walls of the address electrodes 6 and the barrier ribs 7, which is formed by a top part of the barrier rib 7 touching the cathode film 4, and this discharge chamber formed is filled with a mixed gas of neon and xenon (Ne--Xe gas).
Conventional manufacturing process of the plasma display panel shown in FIG. 1 is described below.
To begin with, a flow of manufacturing the frontal glass substrate 5 is performed in three steps of 1) to 3) as described below.
1) In step 1, a method of pattern formation in a thin film photolithography process, or a processing technology such as a thick filmprinting method is usedto form the sustaining discharge electrodes 1x and 1y and the bus electrodes 2x and 2y on the frontal glass substrate 5.
2) In step 2, the dielectric layer 3 is formed by spreading and sintering a thick film glass with a low-melting point.
3) In step 3, the cathode film 4 is formed by vaporizing MgO in a vacuum.
Following is a flow of manufacturing the rear glass substrate 9, performed in steps 4) to 6) as described below.
4) In step 4, the method of pattern formation in the thin film photolithography process, or the processing technology such as the thick film printing method is used to form the address electrodes 6 on the rear glass substrate 9.
5) In step 5, the barrier rib 7 is formed by spreading and sintering the glass with a low-melting point. It is necessary to have the pattern for processing the barrier rib, for examples, a method of forming a pattern directly by a thick film printing, a method of taking the pattern by sandblasting after spreading a plain layer by the thick film printing, or a method of pre-creating a resist pattern for molding to fill the gutter by the thick film printing.
6) In step 6, a paste which is a source material for the fluorescent bodies is spreaded on the rear glass substrate 9, and the fluorescent bodies 8R, 8G and 8B are formed by burning resinous binders contained in the paste.
Process of combining the frontal glass substrate 5 and the rear glass substrate 9 completed accordingly are performed in steps 7) to 10) as described below.
7) In step 7, spread a sealing glass onto at least one of the glass substrates from the frontal 5 or the rear 9, for pasting the two substrates together at the outer edge.
8) In step 8, both substrates are aligned face-to-face.
9) In step 9, the substrates are aligned and pasted at the outer edge by melting the sealing glass with heat. At the same time, an operation to join a chip pipe with the sealing glass (as required later in step 10) is performed against an exhaust vent that is penetrating through the rear glass substrate 9.
10) In step 10, the chip pipe is connected to an air exhaust pipe of an exterior apparatus, and a chamber between the substrates are evacuated through the chip pipe by heating and degassing. After the evacuation is completed, the Ne--Xe gas for discharging is filled inside this chamber through the same chip pipe. When the gas has been filled-up completely, the chip pipe is chipped-off at a point closest to the rear glass substrate 9.
On a surface of the dielectric layer 3 which is obtained by sintering of the glass with low-melting point, generally, a numerous number of minute protrusions at sub-micron to few micron level appears due to a material constituent of the dielectric layer 3 being used. In addition, when a foreign substance became trapped inside the low-melting point glass during the sintering process, this results in an appearance of protrusions in few tenth of micron level at the surface. Even if the cathode film 4 covers the dielectric layer 3, however, since the cathode film 4 is uniform in thickness, the surface protrusions of the dielectric layer 3 are left as they are.
Likewise, at a top of the barrier rib 7, the appearance of protrusions due to the material constituent of the barrier rib 7 being used and an inclusion of the foreign substance happens commonly. Because the barrier ribs 7 has a microscopic pattern which is different from the dielectric layer 3, and the height of the barrier rib 7 ranges from 100 to 200 microns which is usually smaller than its width, and such structure in general tends to break easily when subjected to a pin-point pressure.
Under such state, when the top of barrier rib 7 touches the cathode film 4 after the step 8 as illustrated in FIG. 11, there are a number of cases where the barrier rib 7 break-off due to the pin-point pressures being applied from the protrusions of dielectric layer 3 as well as the protrusions of the top part of barrier rib 7. The breaking of barrier rib 7 occurs mostly during the vacuum evacuation of step 10. That is, as the discharge chamber is being vacuum evacuated, an outside air pressure applied to the frontal glass substrate 5 and the rear glass substrate 9 will be supported by the barrier rib 7 and this will often cause the tips of barrier rib 7 to break.
FIG. 11 illustrates the state of barrier rib breakage in cross-section viewed perpendicularly from the pattern of barrier rib 7. Numbered components indicated in FIG. 11 follows: a foreign substance 21 buried inside the dielectric layer 3; a fracture 22 of barrier rib (7) resulted from receiving the pin-point pressures from the protrusions formed by the inclusion of foreign substance; and a broken fragment 23 from the barrier rib 7. The broken fragment is attaching a little bit of fluorescent body attached to the wall. Such breakage of the barrier rib will cause the dot imperfections at a time of emissive display as described in (a) and (b) of below.
(a) A function of separating the discharge chamber is lost at the fracture 22 of barrier rib, and in FIG. 11, a mutual interference become intensified on right and left sides of the fracture 22. PA1 (b) The broken fragment 23 from the barrier rib becomes physical and electrical obstructions in the discharge chamber. PA1 temporary aligning the first glass substrate and the second glass substrate face-to-face, with a side of the barrier rib facing a side of the dielectric layer; PA1 decompressing a barrier rib pattern area formed with the first and the second glass substrates under the temporary aligning from a normal atmospheric pressure; PA1 cleaning at least one of the glass substrates on facing side after detaching the glass substrates from the temporary aligning, after returning a pressure inside the barrier rib pattern area to the normal atmospheric pressure; and PA1 sealing the discharge chamber by re-aligning and then pasting the two glass substrates in approximately the same manner as the temporary alignment. PA1 an air-tight material for covering over at least one of the glass substrate under the temporary alignment, and PA1 a table for supporting the other one of the glass substrates, and for forming an air-tight space with the air-tight material.
Conventionally, the manufacturing method of the panel display is performed in a manner described previously, that there is a problem of barrier rib breaking in a final stage of the product to cause the dot imperfections at the time of emissive display due to the broken remnants left behind.
In attempt to reduce the occurrence of dot imperfections, reducing the protrusions at the top of barrier rib 7 is effective. A specific method to reduce the protrusions at the top of barrier rib 7 is to polish its surface, however, finishing touch of polishing should be done in a great accuracy otherwise outside air pressure cannot evenly be distributed at the time of vacuum evacuation in step 10, therefore, a prevention of the barrier rib breakage for this reason is difficult.
What's more, even if the protrusions at the top of barrier ribs 7 are completely removed this way, an effect of preventing the barrier rib breakage is still small, since the surface protrusions are also present on the dielectric layer 3.
As means to control the surface protrusions of the dielectric layer 3, conventionally, a prevention of the inclusion of foreign substance during the processing is most effective, in addition, when the protrusions appear at its surface, the surface polishing is also effective. However, practically speaking, it is impossible to control the inclusion of foreign substance for such structure as the panel display involving large area, as well, the surface polishing of the dielectric layer 3 is equally difficult as the polishing of the barrier rib 7.
In order to solve the problem, taking that it is inevitable to prevent the breakage of barrier ribs 7, the present invention aims to reduce the occurrence of dot imperfections by adding a process to a manufacturing apparatus, which is the process to eliminate the broken fragments into the discharge chamber so that the fragments do not become obstruction in the discharge chamber.